The 15 Most Important ETFs

[Editor's Note: This version has been corrected to state that GLD was the first ETF launched in the U.S. to hold physical gold; it was not the first-ever launched of such.]

People have been using gold for millennia. The yellow metal's roots as jewelry and money can be traced all the way back to ancient Egypt, some 5,000 years ago. Gold's reign as the top currency lasted all the way until the last century, when it was finally jettisoned in favor of fiat money.

But gold is still valuable. People remain instinctively drawn to the metal, and its luster is unlikely to wear off any time soon. In fact, millions of ounces of gold continue to be bought every year, and not just for decorative purposes.

Indeed, much of the demand for gold now comes from investors who see the metal as a stable store of value. But rather than buying physical gold bars or coins, these investors are buying up SPDR Gold Shares (GLD | A-100), the revolutionary exchange-traded fund that has brought the ancient metal into the 21st century.

Launched in 2004 by State Street Global Advisors, GLD was the first ETF in the U.S. to hold physical gold. It was an instant hit, gaining more than $1 billion in assets in less than a week, a record that still stands today.

"It's transformed the way people think about gold and investing in gold," said World Gold Trust's CEO Will Rhind. "It also opened the door for investing in commodities more broadly as an asset class, which has become a key portfolio component over the last 10 years."

In fact, since GLD's launch a decade ago, more than 100 commodity ETFs have followed, and today the category boasts more than $50 billion in total assets.

That said, it certainly hasn't been a smooth ride for GLD. The fund's fortunes have waxed and waned based on the demand and price outlook for gold. At one point in 2011, as gold prices were peaking at a record high of $1,921, GLD briefly became the world's largest ETF, with $77.5 billion in assets.

Since then, assets have been slashed to $25 billion amid a combination of outflows and plunging gold prices. Nevertheless, the fund remains the largest and most liquid gold ETF by far.

Gold may be down, but it's not out. If history is any guide, peoples' fascination with the yellow metal isn't going away any time soon, and that means GLD is here to stay.